Capacitor testing

[zachtheterrible]

Hi, I made a metronome to test capacitors. It goes click click, if you have a big capacitor like 10 uf, or it wines if you have something like .01 uf. Anyways, i used it to test the capacitors on a circuit that I made (that doesn't work). Is this a good idea? I compare the sound of two of the same value caps: one that i know is good, and the one that i am testing. Is there any other way to test capacitors w/o buying testing equipment? I'm a little low on funds. Thanx

 

[Nigel Goodwin]

Hi, I made a metronome to test capacitors. It goes click click, if you have a big capacitor like 10 uf, or it wines if you have something like .01 uf. Anyways, i used it to test the capacitors on a circuit that I made (that doesn't work). Is this a good idea? I compare the sound of two of the same value caps: one that i know is good, and the one that i am testing. Is there any other way to test capacitors w/o buying testing equipment? I'm a little low on funds. Thanx

There are various tests you can apply, a simple bridge can be used to measure their value, or (like you have already) you can use them in an oscillator - where the frequency indicates their value.

Another test is leakage, you apply a high voltage and measure the leakage current - obviously the voltage needs to be switchable so you can test different ratings. This was probably more important in the old valve days!.

The most common test these days is probably ESR (Effective Series Resistance) on electrolytics, it's a huge problem with modern electrolytics, probably the major cause of faults these days.

But your oscillator test is probably fairly useful (and fun!), and fun is what it's all about really!.

 

[Johnson777717]

Zach, that is a neat idea! I've never seen someone create an oscillator for that purpose (That doesn't mean that it hasn't been done).

Did you brainstorm the idea yourself, or were you inspired by someone elses circuit? If you brainstormed the idea yourself...good thinking man! Simple and effective.

I am astonished at the thinking power many people have. (Look at me, I'm talking like I'm 78 years old) Still, there's a lot of people who have a talent for thinking and engineering. Ones that I would love to work along side. Good stuff man, keep it up!

I have a schematic of a digital capacitance adaptor for measuring the capacitance value of caps from 2pF on up to 10uF I believe. The adaptor can plug into a digital voltmeter set to a 2volt scale, and output the capacitance of the cap under test. You can also use a panel meter instead of a DVM if you want a stand-alone unit. OR you can make a LED/LCD display using an Analog to Digital converter (ICL7107 etc). Lots of options for customizing the display portion. I can send it to you if you like.

Also, there's a schematic for an ESR tester here, I think I may end up building this little beauty if I can figure out the value for R1 and a suitable OPamp part number:

www.albany.net/~gwoods/esr_meter/esr_meter_index.html

 

[Dean Huster]

ESR

Zach, for some reason, ESR (effective series resistance) has been touted lately as the ONLY decent test for capacitors by some folks. You know, we old timers have been checking caps for a long, long time before "ESR" became such a buzz word. In the vacuum tube days, a value check and a leakage test was more definitive than anything else and we did it with RC bridges that set us back $24.95 new!

Low on funds? You can't be so low that you can't bid on ebay for a Knight-Kit KG-670 or EICO 950B or other kit RC bridge that you can probably get for a song. A couple more bucks to refurbish it and you'll have a decent instrument that'll be really handy on the bench.

ESR is more of a problem with modern, high-current, solid state circuits where the ESR can cause a significant voltage drop within the cap. ESR is rarely a problem (an increase in ESR) with anything other than electrolytic caps anyway.

Dean

 

[Nigel Goodwin]

Re: ESR

Zach, for some reason, ESR (effective series resistance) has been touted lately as the ONLY decent test for capacitors by some folks. You know, we old timers have been checking caps for a long, long time before "ESR" became such a buzz word. In the vacuum tube days, a value check and a leakage test was more definitive than anything else and we did it with RC bridges that set us back $24.95 new!

Those days are long gone :lol: checking for positive grids, fond memories 8)

Almost all capacitor failures these days are electrolytics with low ESR, you can't find these with a bridge (they still read the same value), or with a leakage test (they don't leak any more than normal). You can easily find them with an ESR meter, in circuit as well, or you can find them by measuring the ripple with a scope - which is what I did before I built an ESR meter.

I suspect the main problem is down to the cheaper manufacturing of electrolytics, and the widespread use of switch-mode power supplies. But mostly cheap capacitors, the older switchmode supplies didn't have any where near as many problems!.

 

[zachtheterrible]

Thanx for all the feedback. I didn't understand half of the tests u were talkin about though (never heard of 'em).

What is effective series resistance?? I looked @ johnson's circuit (thanx) but didnt understand it. By the way, i did think up the idea myself 8) , although i got the circuit out of a book. a neat little mod i made to the circuit is i took some . . . wuddya call 'em? ic jumpers? u know, the things you solder into a circuit and then you can plug in different ic's. Anyways, i cut them so that you can plug caps into them.

I didn't quite get how to do a leakage test, could u explain that a little more nigel?

Lastly, wut is a bridge? is a bridge the same as an rc bridge? As for bidding, i'm only 15 and dont have a job . Hopefully, i'll be gettin' one doing general contracting though !!

Thanx a LOT for all the feeback

 

[Nigel Goodwin]

Thanx for all the feedback. I didn't understand half of the tests u were talkin about though (never heard of 'em).

If you don't understand them, you probably don't need them :lol:

What is effective series resistance?? I looked @ johnson's circuit (thanx) but didnt understand it.

It's simply the impedance (AC resistance) of the capacitor at 100KHz, it looks like a low value resistance - the lower the value the better, and (obviously) the bigger the capacitor the lower the value.

It's more important for servicing than just testing capacitors out of your junk box.

I didn't quite get how to do a leakage test, could u explain that a little more nigel?

Simply apply a high voltage to the capacitor, and measure the current with a milliammeter - but again, it's probably not a test you really need, it was far more important back in the valve days.

Lastly, wut is a bridge? is a bridge the same as an rc bridge? As for bidding, i'm only 15 and dont have a job . Hopefully, i'll be gettin' one doing general contracting though !!

Yes, an RC bridge is one that does resistors and capacitors, you can get them that do inductors as well. Basically a bridge compares one value with another, you have a variable control which you adjust for a null, you can then read the value off the scale.

 

[Dean Huster]

Still, Nigel, ESR is not nearly the bugger for a 30µF cap in a 350v, 60ma supply that it is when working with 100,000µF (100mF) in a 5v, 50A supply where the cap is moving a lot of current where the I²R drop of the ESR becomes a significant factor compared to the supply voltage.

I'll be that bad caps show up a lot more often today because of switchers where there's little secondary DC regulation. In the 1970's where linear regulation of each individual supply often compensated for increasing ripple, bad caps in the raw supply often went undiagnosed long after they should have been replaced. More than once, you didn't see DC supply ripple in a Tek oscilloscope unless the raw supply filter cap was darned-near open!

One must look at the situation, too. A marginal cap in a power amp or table radio isn't noticed while one in an audio preamp or mixer may show up quickly.

Still, I've been messing with electronics as a hobby and/or professionally since around 1962, and haven't found that I've been hindered by the lack of an ESR meter. If I had to put the cap test items I'd want in order of importance, a cheap bridge would be at the top of the list since it can measure value and check leakage; then would come the ESR meter. I can own ten ESR meters and won't be able to make the other two tests with them.

For that matter, I've also done OK without an RF sweep generator, a flutter meter, an IM distortion analyzer .....


Dean

 

[zachtheterrible]

ahh, i understand now. i think (for the time being) that ill just stick w/ my trusty ol' metronome

 

[Nigel Goodwin]

Still, Nigel, ESR is not nearly the bugger for a 30µF cap in a 350v, 60ma supply that it is when working with 100,000µF (100mF) in a 5v, 50A supply where the cap is moving a lot of current where the I²R drop of the ESR becomes a significant factor compared to the supply voltage.

It's true it's no where near as important for high voltage capacitors, in fact many high voltage caps have a high ESR when new. But for normal low voltage capacitors, 1uF upwards, an ESR meter will help you find the faulty ones very easily. They do it in circuit, and find the main failure cause, which other methods (apart for a scope) don't find.

Still, I've been messing with electronics as a hobby and/or professionally since around 1962, and haven't found that I've been hindered by the lack of an ESR meter.

If you don't do servicing you probably wouldn't notice the lack, I've been scoping PSU capacitors for ripple for many years, an ESR meter just makes it so much simpler - and they are pretty simple to make!.